1. Field of the Invention
The invention relates generally to methods for making carbon nanotubes and, more particularly, to a method for making an array of carbon nanotubes.
2. Discussion of Related Art
Carbon nanotubes (CNTs) produced by means of arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima, entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). CNTs are electrically conductive along their length, chemically stable, and each can have a very small diameter (much less than 100 nanometers) and large aspect ratios (length/diameter). Due to these and other properties, it has been suggested that CNTs can play an important role in fields such as microscopic electronics, field emission devices, thermal interface materials, etc.
Generally, there are three conventional methods for manufacturing CNTs. The first method is the arc discharge method, which was first discovered and reported in an article by Sumio Iijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). The second method is the laser ablation method, which was reported in an article by T. W. Ebbesen et al. entitled “Large-scale Synthesis of Carbon Nanotubes” (Nature, Vol. 358, 1992, pp. 220). The third method is the chemical vapor deposition (CVD) method, which was reported in an article by W. Z. Li entitled “Large-scale Synthesis of Aligned Carbon Nanotubes” (Science, Vol. 274, 1996, pp. 1701). The CVD method is advantageously useful in synthesis of an array of carbon nanotubes and is advantageous in mass production, improved length controllability, compatibility with conventional integrated circuit process, etc.
Generally, mainly three CVD methods, i.e. the thermal CVD, plasma-enhanced CVD and laser-induced CVD, have been developed for the synthesis of arrays of carbon nanotubes. In conventional laser-induced CVD method, an opaque substrate such as silicon with catalyst is disposed in a closed reactor filled with reactant gases, and either argon ion laser or CO2 laser are employed to directly irradiate laser light on the substrate to heat the substrate to reaction temperature. By locally laser-heating the substrate, carbon nanotubes can be synthesized on the substrate.
However, the above-described laser-assisted CVD method is performed at a closed reactor filled with reactant gases. Thus, the above-described method required a complicated reaction device, and it is difficult to build a huge reactor device for CVD growth of carbon nanotubes on large area substrate. Moreover, the newly grown carbon nanotubes will directly experience an intense laser field which will damage the newly grown carbon nanotubes. Thus, the morphology of the obtained carbon nanotubes will be damaged. These carbon nanotubes do not sufficiently exhibit the useful properties of an array of carbon nanotubes.
What is needed, therefore, is to provide a laser-induced chemical vapor deposition method for making an array of carbon nanotubes, in which the above problems are eliminated or at least alleviated.